Get it 'Right the First Time' With 3D STEP Models
January 12, 2011 |Estimated reading time: 5 minutes
PCB design tools haven’t changed much in the past 20 years. We are using the same basic PCB tools that we used in the 20th century (see Figure 1). What is different, then?
Sure, we have BGAs now and parts so small that they are hard to see with the naked eye. But the CAD tool really doesn't care about size – we just zoom in and the parts and traces are bigger again. What has really changed?
Time. We have far less time to get the job done and fewer chances to get the job done right. Some people even talk about the need to avoid prototyping -- the design must be “designed and launched straight into production.” Most designers would agree that if a board is designed “right the first time,” we can cut down on the time and investment needed to launch a new product.
Figure 1. Is this a screen shot from a 1980s PCB tool or a modern one? From the perspective of wiring parts on a board, the basic PCB tool interface has changed little for decades.
As engineers and designers, when we aren't sure if something is right, we test to see if our design has the proper form, fit and function. Historically this has been done with expensive, time-consuming prototype cycles. We have traditionally designed a board and then built actual hardware that tested the form, fit and function -- correcting what didn't work along the way and repeating the cycle as required.
Fortunately, we now have simulation tools for software and hardware that allow us to do quite amazing, accurate work before we build the actual hardware. But we have been lacking this same tight integration for transferring data from CAD tools into the mechanical domain.
Bridging the ECAD/MCAD Divide WIth 3D Models
For decades, we have used DXF data transfer to move our PCB shapes into the mechanical engineering world where the final mechanical assembly could be created in software before committing to actual hardware. This has required PCB designers to be dependent upon the mechanical engineering group (if we even have these resources to work with), and in this global development environment, they might be 12 time zones away.
There is nothing inherently wrong with this arrangement, but it prevents the designer from receiving one all-important entity: Immediate feedback. We faced a similar problem when we generated Gerber files and sent them off to the board shop to run through its expensive CAM tools to check the film against their process design rules. Now, low-cost CAM tools let us perform these same checks on our desktops and fix problems before we sent the job out, resulting in fewer engineering holds and providing designers with immediate feedback.
Such feedback is the key to increased productivity, fewer errors and faster cycle times. It allows us to immediately see the results of our work and immediately fix issues as they crop up. And immediate feedback has traditionally been lacking when moving CAD data to the mechanical domain.
In the last few years, we have transferred our PCB data (usually via DXF) to the mechanical engineers, who have placed the very minimum of parts on the boards. This usually amounted to the I/O connectors and perhaps a few big or tall components to check for overall clearance issues.
Figure 2. Altium Designer allows the importing of 3D STEP bodies or the creation of relatively complex bodies using extruded shapes such as cylinders and polygons to make up the basic “visual footprints” for the parts that we place on our boards. The white SMA connector was provided by Samtec, and the gold edge launch connector was modeled entirely within AD.
Now, the Altium Designer series [1] offers the next step in this productivity chain: Tight integration with 3D STEP models. (I have a license for Altium, but other tools have this capability. And in the last year, the number of third-party companies that supply free STEP models of their parts has skyrocketed.)
AD integrates FPGA code and board design tightly. It also allows us to visualize our PCBs in 3D. All of our PCB components can then be modeled as simple 3D extrusions that can be assembled into fairly complex shapes or imported as 3D STEP bodies, which most 3D CAD packages can export to (Figure 2).
Previously, the required 3D bodies of standard cases, chassis components and hardware pieces were not readily available. As a result, using the 3D capability to its fullest potential required transferring the design to the ME group to “fit together” the completed soft design.
Figure 3. Parts makers such as Hammond Manufacturing [2] supply 3D STEP models that can be directly imported into design tools like Altium Designer. This allows board designers to check PCB fit directly in the PCB design tool instead of exporting to a mechanical CAD tool. AD also performs rules-based clearance checks and warn if a part on the board hits a part of the imported STEP model.
Recently though, this has started to change. Many chassis and hardware parts companies have begun to supply 3D STEP models of their parts. The intended use is mostly targeted to the ME community for use in the 3D CAD programs, but we as board designers can now put this trend to good use.
Figure 4. Altium Designer provides a final piece of the design process: The ability to fully assemble and visualize our design, when we need it.
With tools like AD, we can import not only the 3D PCB mounted parts, but we can now import the entire mechanical housing in many cases. Companies such as Hammond Manufacturing [2], Samtec [3] and others [4] are providing full 3D models of nearly all of their parts.
Yes, PCB design tools are actually evolving over time. As more parts manufacturers begin to supply 3D STEP models and more design tools are capable of importing them, PCB designers are that much closer to getting it "right the first time.”
References
1. The Altium Designer PCB/FPGA design package is available at www.Altium.com.
2. Hammond Manufacturing supplies a number of 3D STEP bodies for their enclosure product line. Visit www.HammondMfg.com.
3. Samtec supplies an ever-increasing supply of 3D STEP models of connector bodies at www.Samtec.com.
4. A free and growing source of 3D bodies is available at 3D Content Central: www.3dcontentcentral.com.
Steve Hageman has always looked for ways to decrease the cycle time and improve the accuracy of his designs. He designed his first PCB in AutoCAD back in 1986, and he hasn't looked back at doughnut pads and tape since. Currently Steve serves a variety of clients designing and building virtual instruments and other electronic products with the goal of “straight to production” always in mind. Contact Steve at steve@analoghome.com.